This invention relates to the art of monitoring the hydrostatic pressure of drilling fluid in the mud separator to adequately suppress the differential changes of the formation pressure encountered during oil and gas well drilling operations. More particularly, it relates to monitoring parameters associated with the mud separator correlatable to the minimal hydrostatic pressures of the drilling fluid against the formation pressure necessary to avoid blowout hazards.
The invention further relates to monitoring parameters in air drilling operations to determine the volume of injected gases and formation gases being circulated and avoid hazards of formation gases entering the aqueous liquid pit.
Accepted drilling operations utilize drilling fluid or xe2x80x9cmudxe2x80x9d to provide hydrostatic pressure against the formation pressure to prevent the formation pressure from exceeding the hydrostatic pressure of the mud and consequently causing a blow out of the well. In the drilling procedure for oil and gas wells it is common to circulate mud through the hollow drill stem, beyond the drill bit and return it between the drill stem and bore hole or casing. Upon return of the mud to the surface it is transferred to a mud settling pit to settle out the solid cuttings and the mud is recycled. Generally, the mud is processed through a mud separator before going to the mud settling pit. The function of the mud separator is to separate entrained gas from the mud and the solid cuttings and prevent gaseous hydrocarbons from entering the mud pit which could create a disastrous hazard if hydrocarbons got into the mud pit and were ignited. It should be noted that quantities of oil entrained in the mud are not separated at the mud separator. In most cases removal of oil from the mud is a separate operation.
In air drilling operations the mud separator is used to separate aqueous liquids, which are used in air drilling operations to provide lubrication of the drill bit, from injected gases and formation gases and further permits disposal of the formation solid cuttings.
Not only is well blowout a hazard in oil and gas drilling operations, but also blow over into the mud pit from the mud separator if the gas pressure in the separator exceeds the hydrostatic pressure of the mud leg in the mud separator. This could occur if preventative or corrective action is not taken timely.
Some present drilling operations are conducted where the hydrostatic pressure of the mud is less than the formation pressure, which is frequently referred to as under balanced drilling. Such operations increase the bit penetration rate, with a generally longer bit life thus decreasing the cost of drilling the well and decreases the risk of fracturing a low pressure formation by forcing drilling mud into the formation. Thus, it is certainly desirable in drilling operations to conduct under balanced drilling.
Often in drilling oil and gas wells extremely high pressure gas pockets will be encountered with the potential of the well blowing out. However, frequently the high pressure pockets are of such a low porosity that even though high pressure exists in the pores of the strata not enough of a volume of the high pressure gas gets into the well bore to cause an immediate concern. Such encounters of high pressure pockets are reflected in the mud returned to the surface as entrained gas which lessens the density of the drilling fluid and consequently the drilling fluid exerts less hydrostatic pressure. Further, when liquid hydrocarbons are encountered the hydrocarbons further reduce the density of the drilling fluid. When such drilling fluids reach the mud separator the density of the drilling mud may very significantly from the initial density thus the density of the drilling mud in the mud separator may have a density of 95% of the original density.
U.S. Pat. No. 3,365,009 issued to Burnham discloses a method having flow parameter regulating means for controlling the flow rate and pressure of drilling fluid emanating from a well and gas separating means for liberating gas entrained in the fluid prior to recirculating. The regulating apparatus includes a bladder valve with an actuating chamber which receives compressed gas for flexing the resilient bladder to achieve the desired size of the control passageway through the bladder, thus the pressure ratio across the bladder valve may be varied by varying the control passageway.
U.S. Pat. No. 5,010,966 issued to Stokley teaches a method of receiving a return of drilling fluid from a well being drilled, in which the hydrostatic pressure of the drilling fluid is less than the formation pressure, and controlling the flow and pressure of the return, separating oil and gas from the drilling fluid at the surface, and then returning the drilling fluid to the well and separating the oil and gas phases for further disposition.
U.S. Pat. No. 2,314,169 to Wilson discloses a method for detecting gas in well drilling fluids and in particular a method and apparatus for separating and detecting the minute amounts of gas in the drilling fluid during drilling for determining the location of the strata source of the gas.
U.S. Pat. No. 3,213,939 issued to Records discloses a method and apparatus which involves maintaining a desired back pressure on the drilling fluid or mud by means of a controlled gas pressure, which pressure together with the column of drilling fluid assure that a well blow out is prevented.
U.S. Pat. No. 3,498,393 issued to West discloses a method of blow out protection wherein the mud returned to the surface is introduced into a separator and gases retained in the mud are separated from the mud. The gas is then passed through appropriate size lines wherein instruments are located which measure the volume of gas flow by such measurements the operator is appraised of increases and decreases of gas flow rates in sufficient time to take appropriate action as required. The system is designed for drilling operations in which the least possible hydrostatic head is maintained by the drilling fluid.
Assuming constant permeability of the gas strata, from which the gas in the return mud emanates, the flow rate of the gas from the mud separator is comparable to the pressure in the bottom of the well. Comparing the flow rate measurements of the gas from the separator with measurements taken earlier, the rate of change in the flow rate of the gas from the mud separator may be determined. These measurements thus allow the driller to predict what is happening down hole at any given time and then adjust the hydrostatic head by increasing or decreasing density of the mud.
The present invention provides an integrated system that uses the latest electronic and computer technology to provide reliable, instantaneous conditions of drilling fluid and entrained hydrocarbons in the mud separator whereby the drilling operation can be adjusted accordingly. Of particular importance, the invention utilizes the measurements of the hydrostatic pressure of the mud in the mud separator thus detecting changes in the density of the mud returned from the well bore and a significant change of the hydrostatic pressure in the well bore. The gas pressure transducer in the mud separator reading is compared with the hydrostatic pressure of the mud leg in the mud separator to assess the possible blow dry of the mud separator with gas reaching the mud pit. Likewise, the flow rate of the mud from the well bore can be decreased to prevent blow over of the gas into the mud pit and possibly causing a hazard.
In another aspect of the invention, the drilling operation is conducted using air with or without additional nitrogen for drilling operations, in which case, the drilling operation is monitored with pressure and temperature transducers in close proximity to each other in the flare line near the drill site and second pressure transducer in the flare line near the discharge disposal unit which may be a flare or other control burning. Using this latest air drilling technique avoids the necessity of using drilling fluid or mud and consequently the mud pit is maintained to shut-in the well for installation of casing and under emergency situations requiring immediate shut down of the drilling operation and xe2x80x9ckillingxe2x80x9d the well to prevent blowout in case the downhole pressure exceeds the air drilling pressure.
More particularly the present invention provides a monitoring system using electronic transducers to obtain data to calculate the volume of gas and determine the gas pressure and the hydrostatic pressure of the mud leg in the mud separator on a continuing basis thus informing the field personnel of conditions that may or may not require immediate response. The system utilizes transducers at certain locations to obtain gas pressures and hydrostatic pressures of the drilling fluid which a computer analyzes.
In addition, the present invention provides a monitoring system utilizing electronic transducers to obtain data to calculate the volume of formation gas and determine the gas pressure at the well bore on a continuous basis thus informing the field personnel of conditions that may or may not require immediate response. All of which can be done without the use of drilling mud and monitoring of a mud separator.
An object of the invention is to provide continuous data to a computer for calculating gas volumes utilizing the F. H. Oliphant formula (Practical Petroleum Engineers"" Handbook, Third Edition, page 632) or other recognized formulae, and determining the hydrostatic mud leg by the formula p=0.052 dh where xe2x80x9cpxe2x80x9d is the hydrostatic head in p.s.i., xe2x80x9cdxe2x80x9d is the density of the drilling mud in lbs. per gallon and xe2x80x9chxe2x80x9d is the height of mud leg in feet. Preferably, a pressure transducer may be placed at the bottom of the discharge of the mud separator to directly obtain the hydrostatic pressure of the mud in the mud separator. Further, gas retention percentiles are derived from a transducer in the mud section of the mud separator. The transducer reading of the mud leg hydrostatic pressure is subtracted from the calculated mud leg hydrostatic pressure of the mud density in use. The difference is divided by the calculated mud leg hydrostatic pressure and multiplied by 100 to obtain the gas retention percentage. Using the gas retention data and incorporating the Drillpro(copyright) method of gas expansion calculation, a more accurate bottom hole pressure can be obtained.
An additional object of the invention is to collect and analyze adequate data to obtain for injected gases or air drilling with treated water the calculated initial and corrected volume of injected gases, the calculated volume of injected gases, and the total volume of injected and formation gases, then adjusting the volume of injected gases and formation gases for the corrected volumes by correcting for the formation gases specific gravity and the injected gases specific gravities that more accurately ascertain the formation gases volume and injected gases volume that constitute the total volume of formation and injected gases whereby the design engineered volume of gases is maintained with the total volume of formation and injected gases necessary to regulate the pressure of the gases during drilling with the minimum of injected gases.
A further object of the invention is to collect and analyze adequate data to obtain the volume of formation gas from an oil or gas well being drilled by injected gases or air techniques with air and nitrogen or other gases and treated water using the Weymouth modified formula (Practical Petroleum Engineers"" Handbook, third edition, page 912) in a series of unique calculations to determine the entire volume of injected gas and formation gas circulation and allocate the total volume between injected gas and formation gas.
Another object of the invention is to use the latest electronic and computer technology for monitoring data from transducers to give instantaneous readings of changes in the mud separator gas and hydrostatic mud leg pressures thereby enabling control of the drilling operation by appropriately adjusting chokes and pump rates.